Study On The Interharmonic Source Identification In Electric Power System

With the development of technology, people need the ever-increasing demands for power quality. When the power system was in actual operation, due to the nonlinear load and load fluctuations, harmonics and interharmonics will be emerged. Interharmonics will not only cause damage to the power system like harmonics, but also cause voltage fluctuations, flicker andetc. In order to solve the problems caused by interharmonics, the first thing is to find the sources that generate interharmonics. That is to realize interharmonic sources identification.The study on interharmonic sources identification has just started. Until now, there are few methods were proposed. While methods in identification of harmonic sources and flicker sources have proposed many, including active power method, impedance method, ration method and etc. Thus we can learn from these methods and make use of them in identification of interharmonic sources, considering the similarities among them. However, when both the grid side and user side have the interharmonic with the same frequency, traditional methods may give the incorrect result. Besides, traditional methods never take account of the voltage flicker differences caused by different interharmonics with different frequencies.This paper proposed a novel method in interharmonic sources identification, based on the measurement and converted of electrical parameter. Firstly, conduct the measurement voltage and current with Fourier analysis to obtain the main interharmonic voltage spectrum. Secondly, by means of the system short circuit capacity, calculated fundamental impedance and frequency correction, the equivalent interharmonic voltage sources can be obtained through phasor calculation. Then use the equivalent interharmonic voltage sources to calculate the voltage on point of common coupling separately, considering the circuit topology. That is, the interhamonic sources were identified.In addition, considering the instantaneous flicker sensation differences caused by different frequency interharmonics, a weight factor was proposed to divide the responsibility for different frequency interharmonics. Then, three indicators were proposed:interharmonic voltage, interharmonic power and interharmonic energy to realize responsibility division for different conditions.On the basis of theoretical analysis, a set of physical system for interharmonics identification was designed and developed. The system concludes three parts:PC software, data acquisition system and physical experimental circuit based on the NI signal generator. PC software was developed under the VC environment, its main functions are data processing and interface design. The data acquisition system consists of voltage and current data acquisition hardware circuitry and software control. The connection between PC software and data acquisition system is serial communication. The physical experiment circuit was developed with the NI generator and auxiliary components. The experiment result shows that the system can realize the interharmonic sources identification correctly.